The Sky This Week, 2010 July 13 - 20

The Moon passes a passel of planets...

Saturn, 2010 July 3, 01:58 UTImaged at the U.S. Naval Observatory with the 1895-vintage 12-inch f/15 Clark/Saegmüller refractor

The Moon, fresh from her rendezvous with the Sun over the South Pacific last weekend, returns to the evening sky this week. First Quarter occurs on the 18th at 6:11 am Eastern Daylight Time. During the week Luna’s waxing crescent pays nightly visits to a string of bright stars and planets, making the early evening sky the place to watch most of the week’s action. On the evening of the 14th look for the Moon to the southeast of the brilliant planet Venus as twilight gathers. On the 15th she has shifted to a position some six degrees south of ruddy Mars. The 16th finds Luna about ten degrees below golden Saturn, while the 17th and 18th find her passing the vicinity of the bright star Spica. She ends the week drifting through the stars in the “head” of Scorpius, drawing a bead on the red-tinted star Antares. These close approaches should offer some fine opportunities for budding astrophotographers to hone their sky imaging skills.

The first few evenings of the week offer a chance to enjoy some of the splendors of the summer Milky Way once the Moon sets. Clear skies and distance from city lights are necessary to see the Galaxy in all its glory, but a summer trip to the mountains or the shore can often result in both conditions being met. The basic tools for a successful evening’s observing session are binoculars and bug repellent. Binoculars are a great way to explore the vast star clouds of the Milky Way as well as its embedded star clusters and nebulae. As you sweep over the denser portions of the galaxy above the “teapot” asterism of the constellation Sagittarius, you may notice sudden voids in the countless tracts of stars. These seeming “holes” in the sky are actually clouds of dark material that obscure the light of more distant stars. Well over 300 of these dark regions were catalogued in the early 20th Century by the American astronomer Edward Emerson Barnard, a pioneer in astronomical imaging of the Milky Way.

In the early evening sky no fewer than five bright objects (not counting the Moon) vie for your attention this week. Venus will be the first to catch your eye, appearing in the bright glow of twilight almost immediately after the Sun has set. Early in the week she’s located a few degrees east of the bright star Regulus, lead star in the constellation of Leo, the Lion. You’ll probably need to wait until an hour after sunset to see the star, but once you find it you can watch Venus add another degree of separation each succeeding night. To the east of Venus is the orange-tinted glimmer of Mars, which has the same apparent brightness as Regulus but sports a very different color. By the end of the week Venus will be about halfway between Mars and Regulus in the fading twilight.

Ruddy Mars is also moving briskly to the east, closing in on yellow-hued Saturn. During the course of the week Mars halves the distance between himself and the ringed planet, narrowing the gap from ten to five degrees.

Saturn is very gradually creeping eastward as well, but his nightly progress is almost impossible to detect. By this time next year he will have only ventured as far as the star Spica, the last of our bright evening line-up.

Giant Jupiter now rises before midnight, and late-night skywatchers can begin to train telescopes on him by around 1:30 am once he’s climbed above the haze that typically shrouds the horizons on most warm summer nights. Old Jove will offer a refreshing sight to those of us who have watched the smaller discs of the evening planets over the past several months. The small telescope owner will be treated to a constantly changing surface of turbulent cloud tops, along with the four bright moons discovered by Galileo 400 years ago.